Power transmission

ABSTRACT

A HYDRAULIC PUMP OR MOTOR UNIT OF THE AXIAL PISTON TYPE IN WHICH A SWASH PLATE YOKE IS CARRIED ON TRANSVERSE BEARINGS IN A CUP-SHAPED HOUSING AND THE PISTONS HAVE BALL-JOINTED SHOES SLIDING ON THE SWASH PLATE HAS AN IMPROVED PISTON RETRACTION MEANS COMPRISING A FLAT NOTCHED PLATE ENGAGING ALL OF THE PISTON SHOES AND HOLDING THEM IN A COMMON PLANE PARALLEL TO THE SWASH PLATE. A SECOND ANNULAR RETENTION PLATE IS HELD IN POSITION BY A SERIES OF SHOULDERS ON THE YOKE AND SERVES TO PREVENT DISPLACEMENT OF THE FIRST PLATE DURING START-UP AND UNDER CONDITIONS OF HIGH SPEED AND LOW PRESSURE OPERATION.

Sipf. 20, 1971 J. G. BEREZINSKI 3,605,565

POWER TRANSMISSION I Filed'llarch 15, 1970 2 Sheets-Sheet 1 FIG INVENTOR. JOHN 6. BE RE ZINSKI ATTORNEYS SON-20,1971 J. G. asaszmsm 3,605,565

" rowan TRANSMISSION Filed March 13, 1970 2 Sheets Sheet 2 IN VENTOR. JOHN G. BEREZ/NSK/ flwZL 43 ATTORNEYS United States Patent 3,605,565 POWER TRANSMISSION John G. Berezinski, Livonia, Mich., assignor to Sperry Rand Corporation, Troy, Mich. Filed Mar. 13, 1970, Ser. No. 19,191 Int. Cl. F04b 1/02 US. Cl. 91-504 7 Claims ABSTRACT OF THE DISCLOSURE A hydraulic pump or motor unit of the axial piston type in which a swash plate yoke is carried on transverse bearings in a cup-shaped housing and the pistons have ball-jointed shoes sliding on the swash plate has an improved piston retraction means comprising a flat notched plate engaging all of the piston shoes and holding them in a eommon plane parallel to the swash plate. A second annular retention plate is held in position by a series of shoulders on the yoke and serves to prevent displacement of the first plate during start-up and under conditions of high speed and low pressure operation.

In the construction of axial piston pumps of the inline type, there are numerous arrangements for retracting the pistons on the suction stroke. These include the use of a supercharge pressure on the inlet, individual piston springs, and various cage arrangements for holding the piston shoes, which slide around the swash plate, in a plane common to the swash plate. Typical cage arrangements are illustrated in Carey 1,710,567 and Budzich et al. 3,207,082. Such cages may be maintained in the desired plane either by spring force as in Carey, or by relying upon the pistons on the pressure side of the unit to overcome inertia forces resisting retraction of the pis tons on the suction side. Both of these systems impose limitations upon the top speeds at which such a pump may be operated, and particularly so if the delivery pressure against which the pump is operating drops to a low value.

It is an object of the present invention to provide an improved axial piston pump wherein these problems are overcome by a simple inexpensive construction, and one which is easy to assemble and reliable in operation.

The invention consists of an axial piston pump of the inline type wherein pistons are reciprocated by a swash plate over which a set of ball-jointed piston shoes slide in an elliptical path and having an improved arrangement for maintaining the piston shoes in contact with the swash plate during retractive motion of the pistons; which ar rangement comprises a pair of shoe retention plates encircling the pistons, the first plate having internal recesses for reception of the piston shoes and in contact with each shoe on one or both of its surfaces; the second plate encircling the piston shoes outwardly of their elliptical path and in overlying relation to the first plate, and having means for removably securing the second plate in a fixed relation to the swash plate comprising a circumferentially spaced series of abutment shoulders rigidly associated with the swash plate and facing the swash plate at a predetermined distance; together with a correspondingly spaced series of projections on the second plate rotatably engageable and disengageable with the abutment shoulders, and means for locking the second plate in its position of engagement with the abutment shoulders.

In the drawings:

FIG. 1 represents a longitudinal cross section of an axial piston pump embodying a preferred form of the present invention; the top half of the figure being taken on a central plane and the lower half being taken on a parallel plane offset therefrom.

Patented Sept. 20, 1971 FIG. 2 is an end view, partly in section, of the yoke of the pump of FIG. 1.

FIG. 3 is a side view of the yoke of FIG. 2.

FIG. 4 is a fragmentary view of a piston shoe retention late.

p The principal elements of the pump illustrated comprise a casing 10 carrying a shaft 12 having a coupling 14 at its exterior end. Splined to the shaft 12 is a cylinder barrel 16 carrying a plurality of reciprocable pistons 18. The right end face of the barrel 16 abuts a wearplate 20 which in turn abuts the end closure member 22 of the housing 10. Each piston 18 has a shoe 24 swaged to its outer end by a ball joint. The shoes 24 slide around a flat swash plate 28 which is secured to a yoke 30'. The yoke 30 is oscillatable in the housing 10 by means of its trunnions 32 which turn in bearings 34. The housing 10 is formed as a one-piece, generally cup-shaped member, provided with an opening 36 in which the bearings 38 for the shaft 12 are received. The side walls of the housing 10 are provided with large openings 39 on a transverse axis and which receive the bearings 34. A closure cap 40 and spacer 42 retains the bearings at the top of FIG. 1 and an integral cap and bearing retainer 44 closes the opening at the bottom of FIG. 1. The bearings 34 are preferably of the tapered roller type.

The yoke itself is formed generally as a shallow cup in which the swash plate is received. It has a pair of integral trunnions 32 extending laterally from its side and adjacent to the somewhat larger diameter cylindrical shoulders 46 which are nevertheless smaller in diameter than the openings 39 in the housing 10. The yoke is machined to provide a flat annular face 48 against which the swash plate 28 may be accurately positioned and pinined at a dowel hole 50. The groove 52 may be machined in the walls of the cup to receive a shoe retaining ring 54. The overhanging flange 56 is interrupted at a plurality of points such as 58 so that the ring 54 which has correspondingly shaped cars 59 and 61 may be inserted therein and turned about the shaft axis to lock the ears into the groove 52 and underneath the interrupted flange 56. One of the trunnions is bored at 60 to receive a locking pin '62 which engages a notch 63 in the car 61 to prevent displacement of the retention ring 54. The pin 62 is held in position by the cover plate 40. A second retention plate 65 engages grooves in the individual piston shoes 24 and may be of a construction similar to the cage 60 illustrated in the Budzich Pat. 3,207,082.

The yoke 30 is also provided with a pair of ears 66 adjacent the left trunnion 32 in FIG. 2 and located circumferentially approximately 45 away from it. These are for the purpose of engaging actuators to control the tilt angle of the yoke 30. The ears 66 are provided with interrupted cylindrical recesses 68 within which cylindrical abutments 70 may be inserted end-wise and retained by pins 72. A typical actuator may comprise a cylindrical plunger 74 as shown in FIG. 1 having an end face 76 abutting the cylindrical abutment 70. The plungers 74 slide in bores 78 in the housing member 10 and extend into cavities "80 in the end closure 22 which form, in effect, hydraulic cylinders. Suitable adjustable stop pins 82 may be provided for controlling the neutral or minimum stroke position of the yoke 30.

Since the yoke and the trunnions are constructed of an integral piece, the assembly of the yoke into the cupshaped housing must be done prior to insertion of the bearings 34 into their assembled position. By constructing the trunnions with adjacent shoulders such as 46 which are small enough to enter into the openings 38 in the housing, the yoke may be assembled by inserting it from the open end of the housing 10 in an inclined relationship until one of the trunnions and its adjacent shoulder can enter fully into its opening 38. The opposite trunnion is short enough to swing along the interior wall of the housing until it can enter its opening 38, after which the bearings may be assembled onto the trunnions and into their openings and the end cap 44 installed in place. The revolving group consisting of the cylinder barrel 16, the pistons 18, the shoes 24 and the retention plates 65 and 54 are next assembled as a unit and inserted into the open end of the housing 10. The ears 59 and 61 of the retention plate 54 are placed in alignment with the recesses 58 and when the shoes contact the swash plate 2 8, the plate 54 may be rotated in groove 52 until the slot 63 is opposite the bore 60 in the trunnion. The pin 62 may then be inserted and the cover 40 and spacer 42 secured in place. Thereafter, the remaining elements of the pump may be assembled in usual order.

In the preferred arrangement, te second retention plate 65 does not contact the first retention plate or cage 54 when shoes 24 are all in contact with the swash plate, but instead a slight clearance of .005 or .010 of an inch is provided. This, of course, is determined by the machining of the groove 52 relative to the surface 48 as illustrated in FIG. 3. By this construction, there is no rub bing contact between the two retention plates under the usual conditions. That is to say that when the delivery pressure is sufiiciently high to hold the cage or retention plate 65 with the piston shoes which are under pressure in contact with the swash plate, then automatically the piston shoes which are being retracted must also maintain contact with the swash plate because the cage 65 holds them in a common plane. If, however, during high speed operation the delivery pressure falls to a medium or low value, this pressure acting on those pistons which are subject to it, may be insufiicient to overcome the inertia forces which resist retraction of the pistons on the suction side of the pump. Under these conditions, the retention plate 65 will move slightly away from the swash plate until it contacts the retention ring 54 which will then assure positive retraction of the pistons by mechanical contact. During all other conditions, the cage 64 maintains the retracting piston shoes against the swash plate and there is no rubbing contact between retention plates 65 and 54. The construction thus provides a reliable piston retraction system in an axial piston pump and one which is simple and inexpensive as well as reliable in operation.

I claim:

1. A piston pump of the axial piston type wherein the pistons are reciprocated by a swash plate over which a set of ball-jointed piston shoes slide in an elliptical path and having an improved arrangement for maintaining the piston shoes in contact with the swash plate during retractive motion of the pistons which arrangement comprises a pair of shoe retention plates encircling the pistons, the first plate having internal recesses for reception of the piston shoes and in contact with each shoe on one or both of its surfaces, the second plate encircling the piston shoes outwardly of their elliptical path and in overlying relation to the first plate, and means for removably securing the second plate in a fixed relation to the swash plate comprising a circu'mferentially spaced series of abutment shoulders rigidly associated with the swash plate and facing the swash plate at a predetermined distance, a correspondingly spaced series of projections on the second plate rotatably engageable and disengageable with the abutment shoulders and means for locking the second plate in its position of engagement with the abutment shoulders.

2. A pump as defined in claim 1, wherein the swash plate surface is carried by a cup-shaped member having cylindrical walls surrounding the swash plate surface and carrying the abutment shoulders.

'3. A pump as defined in claim 1 wherein the swash plate is supported in a cup-shaped yoke having radially extending trunnions and the locking means is positioned in one of the trunnions.

4. A pump as defined in claim 1 wherein the abutment shoulders are in the form of an interrupted annulus extending radially inward and the projections on the second plate are shaped to fill the spaces between adjacent shoulders when the plate is being assembled.

5. In a variable displacement axial piston pump having a rotatable cylinder block carrying reciprocable pistons having ball-jointed sliding shoes for actuation by a swash plate, a one-piece housing formed as a cup and a onepiece swash plate yoke journalled in the housing and formed as a shallow cup that improvement comprising a pair of shoe retention plates of generally annular shape, the first plate engaging each of the shoes and revolving with them, the second plate overlying the first plate but not revolving with it and having a series :of radially outward projections on its outer periphery, a series of radially inward abutment shoulders on the yoke facing the swash plate, the space between the abutments allowing the assembly of the second plate with its projections intermediate adjacent shoulders into a position holding the first plate and the shoes against substantial lifting away from the swash plate and being rotatable to engage the projections under the shoulders, and means for locking the second plate against rotation.

6. A pump as defined in claim 5 wherein the locking means comprises a pin mounted in a 'bore in one of the trunnions and extending radially inward to contact the second plate intermediate to the projections.

7. A pump as defined in claim 5 wherein the second plate is normally spaced from the first plate a short distance and acts to limit any rise of the piston shoes during retraction to a small value.

References Cited UNITED STATES PATENTS WILLIAM L. FREEH, Primary Examiner US. Cl. X.R. 9'1-507 

